Ate, ang tummy pain with lots of baby movement can be normal late pregnancy, pero since you're unsure pa ng exact dating at may pain ka, please message your OB or go to your clinic ASAP lang para ma-check properly, okay lang mag-alala, yan ang work nila!
The thing is, dating discrepancies (like your center vs. transv dates) happen often, kaya hindi talaga sigurado kung kailan exact ang ready mo manganak, at ang pain mo needs professional checking lang to be safe. A few of us mums din nag-confuse with dates, pero ang OB lang talaga makakatulong dito, especially FTM ka pa. Wag mag-stress, go see them soon, okay? They'll know what's happening better!